The overall aim of our research program is to contribute toward an understanding of the structure and biological activity of immunoglobulins. In line with this overall objective we are carrying out the following projects: The first line of investigation is concerned with the structure of immunoglobulins. We are developing a general method for preparing specific mercury derivatives of immunoglobulins. In addition, we plan to investigate the properties of an unusual crystallizable myeloma protein that apparently has a deletion in the "hinge region" of the heavy chain. We also wish to determine whether changes in the conformation of antibodies occur upon antigen binding. The aim of the second group of studies is to elucidate the origins of the immune proteins, both in terms of the development of the species (phylogeny) and the development of the individual (ontogeny). We will compare the immune response in tadpoles with that in adult frogs. The third project is a study of the diversity of the immune response, of the manner in which antibodies may be combined to generate the broad range of serological specificities. We shall determine whether a specific antiserum contains any molecules that are actually complementary to (i.e., more reactive with) a ligand other than the immunogen.